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This article will help you find answers to many of your questions about the nature, causes, and prevention of cancer. You can learn about the following topics:

What is cancer?

How is cancer detected and diagnosed?

What causes cancer?

What is the link between genes and cancer?

What is cancer prevention?

Different Kinds of Cancer

Cancer can originate almost anywhere in the body.

Carcinomas , the most common types of cancer, arise from the cells that cover external and internal body surfaces. Lung, breast, and colon are the most frequently diagnosed carcinomas in the United States.

Sarcomas are cancers arising from cells found in the supporting tissues of the body such as bone, cartilage, fat, connective tissue, and muscle.

Lymphomas are cancers that arise in the lymph nodes and tissues of the body's immune system.

Leukemias are cancers of the immature blood cells that grow in the bone marrow and tend to accumulate in large numbers in the bloodstream.

Naming Cancers

Scientists use a variety of technical names to distinguish among the many different types of carcinomas, sarcomas, lymphomas, and leukemias. In general, these names are created by using different prefixes that stand for the name of the cell type involved. For example, the prefix "osteo" means bone, so a cancer arising in bone is called an osteosarcoma. Similarly, the prefix "adeno" means gland, so a cancer of gland cells is called adenocarcinoma -- for example, a breast adenocarcinoma.

Loss of Normal Growth Control

Cancer starts when there is a loss of normal growth control. In normal tissues, the rates of new cell growth and old cell death are kept in balance. In cancer, this balance is disrupted. This disruption can result from uncontrolled cell growth or loss of a cell's ability to undergo "apoptosis." Apoptosis, or "cell suicide," is the mechanism by which old or damaged cells normally self-destruct.

Example of Normal Growth

To illustrate what is meant by normal growth control, consider the outermost layer of the skin. The thin outer layer of normal skin, called the epidermis, is roughly a dozen cells thick. Cells in the bottom row of this layer, called the basal layer, divide just fast enough to replenish cells that are continually being shed from the surface of the skin. Each time one of these basal cells divides, it produces two cells. One remains in the basal layer and retains the capacity to divide. The other migrates out of the basal layer and loses the capacity to divide. The number of dividing cells in the basal layer therefore stays the same.

The Beginning of Cancerous Growth

During the development of skin cancer, the normal balance between cell division and cell loss is disrupted. The basal cells now divide faster than is needed to replenish the cells being shed from the surface of the skin. Each time one of these basal cells divides, the two newly formed cells will often retain the capacity to divide, thereby leading to an increase in the total number of dividing cells.

Invasion and Metastasis

Cancers are capable of spreading through the body by two mechanisms: invasion and metastasis. Invasion refers to the direct migration and penetration by cancer cells into neighboring tissues. Metastasis refers to the ability of cancer cells to penetrate into lymphatic and blood vessels, circulate through the bloodstream, and then invade normal tissues elsewhere in the body.

Tumors (Neoplasms)

The gradual increase in the number of dividing cells creates a growing mass of tissue called a "tumor" or "neoplasm." If the rate of cell division is relatively rapid, and no "suicide" signals are in place to trigger cell death, the tumor will grow quickly; if the cells divide more slowly, tumor growth will be slower. But regardless of the growth rate, tumors ultimately increase in size because new cells are being produced in greater numbers than needed. As more and more of these dividing cells accumulate, the normal organization of the tissue gradually becomes disrupted.

Malignant versus Benign Tumors

Depending on whether or not they can spread by invasion and metastasis, tumors are classified as being either benign or malignant. Benign tumors are tumors that cannot spread by invasion or metastasis; hence they only grow locally. Malignant tumors are tumors that are capable of spreading by invasion and metastasis. By definition, the term "cancer" applies only to malignant tumors.

Why Cancer Is Potentially Dangerous

A malignant tumor, a "cancer," is a more serious health problem than a benign tumor because cancer cells can spread to distant parts of the body. For example, a melanoma (a cancer of pigmented cells) arising in the skin can have cells that enter the bloodstream and spread to distant organs such as the liver or brain. Cancer cells in the liver would be called metastatic melanoma, not liver cancer. Metastases share the name of the original ("primary") tumor. Melanoma cells growing in the brain or liver can disrupt the functions of these vital organs and so are potentially life threatening.

Cancer Detection and Diagnosis

Detecting cancer early can affect the outcome of the disease for some cancers. When cancer is found, a doctor will determine what type it is and how fast it is growing. He or she will also determine whether cancer cells have invaded nearby health tissue or spread (metastasized) to other parts of the body. In some cases, finding cancer early may decrease a person's risk of dying from the cancer. For this reason, improving our methods for early detection is a high priority for cancer researchers.

Early Cancer May Not Have Any Symptoms

Don't wait to feel pain before getting checked for cancer because cancer does not always have symptoms. Some people visit the doctor only when they notice changes like a lump in the breast or unusual bleeding or discharge. However, early cancer may not have any symptoms. That is why screening for some cancers can help, particularly as you get older. Screening methods are designed to check for cancer in people with no symptoms.

Pap Test

A screening technique called the Pap test (or Pap smear) allows early detection of cancer of the uterine cervix. In this procedure, a doctor uses a small brush or wooden scraper to remove a sample of cells from the cervix and upper vagina. The cells are placed on a slide and sent to a laboratory, where a microscope is used to check for abnormalities.

Mammograms

Breast cancer can sometimes be detected in its early stages using a mammogram, an X-ray of the breast. Mammography is most beneficial for women as they age and undergo menopause. Mammography is a screening tool that can detect the possible presence of an abnormal tissue mass. By itself, it is not accurate enough to provide definitive proof for either the presence or absence of breast cancer. If a mammogram indicates the presence of an abnormality, further tests must be done to determine whether breast cancer actually is present.

Blood Tests

Many cancers cannot yet be readily detected in their early stages, but scientists are working hard to find new clues. Scientists are trying to develop blood tests that might alert people to such cancers while they are still in their early stages. For example, several blood tests for ovarian or prostate cancer are under active study.

One example is a substance called prostate-specific antigen (PSA), produced by cells of the prostate gland. PSA circulates in the blood and can be detected and measured with a simple blood test.

Fecal Occult Blood Test (FOBT)

A procedure called a fecal occult blood test (FOBT) detects invisible amounts of blood in the feces, a possible sign of several disorders, including colon cancer. The test is painless and can be done at home or in the doctor's office. With an application stick, a dab of a stool specimen is smeared on a chemically treated card, which is tested in a laboratory for evidence of blood. If blood is confirmed in the stool, more tests may be performed to find the source of the bleeding. Early detection using FOBT may help to decrease mortality from colon cancer.

Biopsy

To diagnose the presence of cancer, a doctor must look at a sample of the affected tissue under the microscope. Hence when preliminary symptoms, Pap test, mammogram, PSA test, or fecal occult blood test indicate the possible existence of cancer, a doctor must then perform a biopsy, which is the surgical removal of a small piece of tissue for microscopic examination. (For leukemias, a small blood sample serves the same purpose.) Microscopic examination will tell the doctor whether a tumor is actually present and if so, whether it is malignant (cancer) or benign.

Microscopic Appearance of Cancer Cells

Cancer tissue has a distinctive appearance under the microscope. Among the traits the doctor looks for are a large number of dividing cells, variation in nuclear size and shape, variation in cell size and shape, loss of specialized cell features, loss of normal tissue organization, and a poorly defined tumor boundary.

Hyperplasia

Instead of finding a benign or malignant tumor, microscopic examination of a biopsy specimen will sometimes detect a condition called "hyperplasia." Hyperplasia refers to tissue growth based on an excessive rate of cell division, leading to a larger than usual number of cells. Nonetheless, cell structure and the orderly arrangement of cells within the tissue remain normal, and the process of hyperplasia is potentially reversible. Hyperplasia can be a normal tissue response to an irritating stimulus. For example, a callus that may form on your hand when you first learn to swing a tennis racket or a golf club is produced by hyperplasia.

Dysplasia

In addition to hyperplasia, microscopic examination of a biopsy specimen can detect another type of noncancerous condition called "dysplasia." Dysplasia is an abnormal type of excessive cell proliferation characterized by loss of normal tissue arrangement and cell structure. Often such cells revert back to normal behavior, but occasionally, they become malignant overtime. Because of their potential for becoming malignant, areas of dysplasia should be closely monitored by a health professional. Sometimes they need treatment.

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